Camshaft including weight reducing features and method of forming

ABSTRACT

A camshaft assembly may include a assembly and a shaft. The cam assembly may include a hollow structure with an interior surface and an exterior surface. A plurality of projections may be located on the exterior surface of the hollow structure. The interior surface of the cam assembly may define a recess axially aligned with at least one of the plurality of projections. At least one of the plurality of projections may define an undercut portion. The cam assembly may be coupled with the shaft.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/720,867, filed on Mar. 10, 2010, the entire disclosure of which isincorporated herein by reference.

FIELD

The present disclosure relates to engine camshafts, and morespecifically to a lightweight camshaft assembly.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

An engine camshaft assembly may include a plurality of projections,e.g., lobes and main bearing supports or journals, located on theexterior surface of a hollow tube. During operation of the engine, thecamshaft assembly is rotated and the lobes act to open the intake and/orexhaust valves of the engine. The journals provide the bearing surfacefor the support of the camshaft assembly of the engine. The mass of thecamshaft affects the efficiency of an engine and, in the case of motorvehicles, fuel economy. Therefore, engine designers typically attempt toreduce the mass of the camshaft assembly by various means.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

A camshaft assembly may include a shaft and a cam assembly coupledthereto. The cam assembly may comprise a hollow structure with aninterior surface and an exterior surface, with a plurality ofprojections on the exterior surface. The interior surface may define arecess axially aligned with at least one of the plurality ofprojections. At least one of the plurality of projections may include anundercut portion.

An engine assembly may comprise an engine structure and a camshaftassembly. The camshaft assembly may include a shaft and a cam assemblycoupled thereto. The cam assembly may comprise a hollow structure withan interior surface and an exterior surface, with a plurality ofprojections on the exterior surface. The interior surface may define arecess axially aligned with at least one of the plurality ofprojections. At least one of the plurality of projections may include anundercut portion.

A method of assembling a camshaft assembly may include providing a shaftand forming a cam assembly. The cam assembly may comprise a hollowstructure with an interior surface and an exterior surface, with aplurality of projections on the exterior surface. The interior surfacemay define a recess axially aligned with at least one of the pluralityof projections. At least one of the plurality of projections may includean undercut portion. The cam assembly may be coupled with the shaft.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustrative purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a perspective view of an exemplary camshaft assembly accordingto the present disclosure;

FIG. 2 is a cross-sectional view of the camshaft assembly shown in FIG.1;

FIG. 3 is a perspective view of an exemplary cam assembly according tothe present disclosure;

FIG. 4 is a perspective view of an exemplary cam assembly according tothe present disclosure;

FIG. 5 is a partially exploded perspective view of an exemplary camshaftassembly according to the present disclosure; and

FIG. 6 is a schematic section view of an engine assembly including anexemplary camshaft assembly according to the present disclosure.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Examples of the present disclosure will now be described more fully withreference to the accompanying drawings. The following description ismerely exemplary in nature and is not intended to limit the presentdisclosure, application, or uses.

With reference to FIG. 1, a camshaft assembly 10 is illustrated. Thecamshaft assembly 10 may include a shaft 12 and at least one camassembly 14. In the example illustrated in FIG. 1, the camshaft assembly10 includes five cam assemblies 14 distributed along the axial length Lof shaft 10. Each cam assembly 14 may include one or more projections16. The projections 16 of camshaft assembly 10 may be, as a non-limitingexample, lobes that are used to operate to open the intake and/orexhaust valves of an engine, as is well-known, and/or journals that areused as main bearing supports for the camshaft assembly 10. In theexample illustrated in FIG. 1, the cam assemblies 14 at each end of thecamshaft assembly 10 include two projections 16 each (one lobe and onejournal) while the three cam assemblies 14 in the middle of the camshaftassembly include three projections each (two lobes and one journal).

As seen in FIG. 2, cam assembly 14 may be a hollow structure, e.g., acylindrical tube, that includes an exterior surface 17 and an interiorsurface 19. Projections 16 may be present on, and extend from, theexterior surface 17. By way of non-limiting example, both the interiorand exterior surfaces 17, 19 may be profiled such that the total mass ofthe cam assembly 14, and associated camshaft assembly 10, may bereduced.

As described above, one or more projections 16 may project from theexterior surface 17 of cam assembly 14. In order to achieve a reductionin mass of the cam assembly 14, all or a subset of the projections 16may include an undercut portion 16U. The undercut portion 16U may beconstructed such that the axial length 16L along the contact surface 16Cof the projection 16 is greater than the axial length 16L′ along theexterior surface 17 of cam assembly 14. Further, the height of theundercut portion 16H may be increased to maximize the reduction of masswhile maintaining the strength, structural integrity and performance ofthe projection 16 and cam assembly 14.

The interior surface 19 may also be profiled in order to reduce the massof cam assembly 14. As seen in FIG. 2, for example, all or a subset ofthe projections 16 may include a recess 15 formed in and defined by theinterior surface 19 of the cam assembly 14. The recess 15 may be axiallyaligned with its associated projection 16. The recess 15 may include arecess depth 15D that may be increased to maximize the reduction of masswhile maintaining the strength, structural integrity and performance ofthe projection 16 and cam assembly 14. The recess depth 15D may varyalong the circumference of the cam assembly 14 such that further massreduction of the cam assembly 14 may be achieved. In one non-limitingexample, the recess depth 15D may vary such that a substantiallyconstant material thickness 15H between the interior recess surface 15Cand contact surface 16C of the projection 16 is maintained.

With reference to FIGS. 3 and 4, the cam assemblies 14 at each end ofthe camshaft assembly 10 are illustrated. In the non-limiting examplesof FIGS. 3 and 4, the cam assemblies 14 may include one or more couplingopenings 140. Coupling openings 140 may be, for example, utilized tocouple the assembled camshaft assembly 10 to an engine assembly.Coupling openings 140 may be hollow recesses that extend axially atleast partially through a projection 16. In order to accommodate thecoupling openings 140, the recess 15 in the projection 16 through whichcoupling openings 140 extend may be interrupted by and includeunrecessed portions 150. Unrecessed portions 150 may be defined by theinterior surface 19 of the cam assembly 14. In this manner, the couplingopenings 140 may be structurally unaffected, while also reducing themass of projection 16 by including a recess 15 in appropriate locations.

With reference to FIG. 5, an exemplary camshaft assembly 10 isillustrated. Shaft 12 may comprise a hollow structure, such as a steeltube, which may be physically coupled with the cam assembly 14. Theshaft 12 may be inserted into one or more hollow cam assemblies 14 andfrictionally engaged with the interior surface 19, such as by theballizing method that is described more fully below. In this manner, camassembly 14 and shaft 12 may be coupled to rotate together.

An exemplary method of manufacturing a camshaft assembly, such ascamshaft assembly 10 described above, is described as follows. A shaft12 may be provided. The shaft 12 may comprise a hollow tube structure,as described above. By way of non-limiting example, the shaft 12 may bea thin walled tube structure that is designed to reduce the mass ofshaft 12, while also maintaining the strength, structural integrity andperformance of the camshaft assembly 10.

A cam assembly 14 may be formed. In a first non-limiting example, thecam assembly 14 may be formed by an investment casting process. Theinvestment casting process may include the step of forming an investmentwithin a shell of a ceramic or similar material. The shell may be filledwith a molten material, e.g., steel, that will be used to form the camassembly 14. Upon cooling of the material, the shell may be removed,e.g., by hammering, vibration, chemical removal or other process.Alternatively, the shell may begin to crack and fall away from the camassembly 14 upon cooling. In comparison to other casting processes, theaccuracy of an investment reduces the amount of machining to completethe cam assembly 14. In a second non-limiting example, the cam assembly14 may be formed by a powder metallurgy (“PM”) process. With a PMprocess, however, the coupling of the cam assembly 14 with the shaft 12(described below) may be accomplished by sinter bonding.

The formed cam assembly 14 may be hardened, for example, by inductionhardening, flame hardening, laser hardening or any other hardeningprocess. The cam assembly 14 as a whole may be hardened or individualcomponents of the cam assembly 14, such as projections 16, may behardened. The hardened cam assembly 14 may then be coupled with shaft12, which is described more fully below.

The cam assembly 14 and shaft 12 may be coupled by being frictionallyengaged with each other, for example, by a ballizing process. In aballizing process, the cam assembly 14 may be positioned on a hollow,tubular shaft 12. The tubular shaft 12 may then be expanded to hold thecam assembly 14 in position. This may be accomplished by clamping theends of the shaft 12 to prevent longitudinal growth and forcing a ball(or plurality of balls of increasing diameter) through the tubular shaft12. The ball or balls are larger than the original shaft 12 innerdiameter, thus expanding the shaft 12 to engage cam assembly 14. Otherforms of coupling the cam assembly 14 with shaft 12 may also be used,such as sinter bonding, welding, shrink fitting, an expanding mandrelprocess or any other method.

It is understood that the parts of the camshaft assembly 10 may becoupled to one another in a variety of ways and the present disclosureis not limited to a frictional engagement. For example, in variousembodiments the shaft 12 may be formed integrally with the cam assembly14 to form a monolithic camshaft assembly 10. In these embodiments, thestep of coupling the shaft 12 with cam assembly 14 may be eliminated asthe shaft 12 and cam assembly 14 may be formed as a single, monolithicpiece.

With reference to FIG. 6, an engine assembly 20 may include an enginestructure 30, a crankshaft 32 rotationally supported by the enginestructure 30, one or more pistons 34 coupled to the crankshaft 32,intake and exhaust camshaft assemblies 36, 38 rotationally supported onthe engine structure 30, valve lift assemblies 44, at least one intakevalve 46, and at least one exhaust valve 50. One or both of the camshaftassemblies 36, 38 may have the structure of camshaft assembly 10described above. In the present non-limiting example, the engineassembly 20 is shown as a dual overhead camshaft engine with the enginestructure 30 including a cylinder head 54 rotationally supporting theintake and exhaust camshaft assemblies 36, 38. However, it is understoodthat the present disclosure is not limited to overhead camshaftconfigurations. An engine block 56 may define cylinder bores 58. Thecylinder head 54 and the cylinder bores 58 in the engine block 56 maycooperate to define combustion chambers 60.

1. A camshaft assembly comprising: a shaft; and a cam assembly coupledwith the shaft, the cam assembly comprising a hollow structure with aninterior surface and an exterior surface, and a plurality of projectionson the exterior surface, wherein: the interior surface defines a recessaxially aligned with at least one of the plurality of projections, andat least one of the plurality of projections defines an undercutportion.
 2. The camshaft assembly of claim 1, wherein the shaft ishollow.
 3. The camshaft assembly of claim 1, wherein the shaft isfrictionally engaged with the cam assembly.
 4. The camshaft assembly ofclaim 1, wherein the cam assembly is integrally formed with the shaft.5. The camshaft assembly of claim 1, wherein the cam assembly ismanufactured by an investment casting process.
 6. The camshaft assemblyof claim 1, wherein the recess includes at least one unrecessed portion.7. The camshaft assembly of claim 1, wherein: the interior surfacedefines a recess axially aligned with each of the plurality ofprojections; and each of the plurality of projections defines anundercut portion.
 8. An engine assembly comprising: an engine structure;and a camshaft assembly including: a shaft; and a cam assembly coupledwith the shaft, the cam assembly comprising a hollow structure with aninterior surface and an exterior surface, and a plurality of projectionson the exterior surface, wherein: the interior surface defines a recessaxially aligned with at least one of the plurality of projections, andat least one of the plurality of projections defines an undercutportion.
 9. The engine assembly of claim 8, wherein the shaft is hollow.10. The engine assembly of claim 8, wherein the shaft is frictionallyengaged with the cam assembly.
 11. The engine assembly of claim 8,wherein the cam assembly is integrally formed with the shaft.
 12. Theengine assembly of claim 8, wherein the cam assembly is manufactured byan investment casting process.
 13. The engine assembly of claim 8,wherein the recess includes at least one unrecessed portion.
 14. Theengine assembly of claim 8, wherein: the interior surface defines arecess axially aligned with each of the plurality of projections; andeach of the plurality of projections defines an undercut portion.
 15. Amethod comprising: providing a shaft; forming a cam assembly, the camassembly comprising a hollow structure with an interior surface and anexterior surface, and a plurality of projections on the exterior surfacewherein: the interior surface of the cam assembly defines a recessaxially aligned with at least one of the plurality of projections, andat least one of the plurality of projections defines an undercutportion; and coupling the cam assembly with the shaft.
 16. The method ofclaim 15, wherein forming the cam assembly comprises an investmentcasting process.
 17. The method of claim 15, wherein the recess includesat least one unrecessed portion.
 18. The method of claim 15, whereincoupling the cam assembly with the shaft comprises frictionally engagingthe cam assembly with the shaft.
 19. The method of claim 15, furthercomprising induction hardening the cam assembly.
 20. The method of claim15, wherein coupling the cam assembly with the shaft comprises aballizing process.